I have tried this sort of thing years ago and got in a mess so I now do a clean install of the OS when I change a motherboard.
You can in theory change it across but all the motherboard drivers would be wrong, it can be solved by doing a windows repair and installing the drivers for the new board. But I tried this and got in such a mess I ended up blanking the hard drive and reinstalling.
Some others have managed it ok but as I said I had bother and found reinstalling from scratch was better. But thats just me.
Now as to whether you can use your old OS it depends on whether its a full version or an OEM version. If its a full version then you can use it again but you will have to revalidate it with Microsoft explaining you have deleted it from your old PC and have installed it on your new one.
If its OEM then Microsoft might refuse to revalidate it as OEM is meant to die with the motherboard, they might allow it they might not.
To find out which you have either refer to your label on your PC or look under CONTROL PANEL ,SYSTEM if the serial number has OEM in it then thats what you have.
Not sure about the LEDs though.